Depanjan Sarkar

Mr Depanjan Sarkar

Research Fellow

Organisation

University of Manchester

Research summary

Introduction of ambient ionization techniques provided ways to understand and manipulate ions for applications and this changed the scope of mass spectrometry beyond analysis. Different chemical reactions were done using mass spectrometry as a synthetic tool. This was named as synthetic mass spectrometry. It was shown that the chemical reactions accelerate in charged droplets. Different named reactions were done using preparative mass spectrometry, which resulted in better product yields as well as orders of larger reaction kinetics over conventional synthetic procedures. Synthesis of hetero-ring compounds like isoquinoline and substituted quinolines were also done easily in microdroplets.

On the other hand, nanoscale materials have been introduced to make ionization easier and better. These modified substrates were used for miniaturization of mass spectrometers. For example, Carbon nanotubes were used as a substrate for molecular ionization at very low voltages. This shows the possibility of nanomaterials in simplifying ionization processes in mass spectrometry. Nanomaterials can be used for ionizing molecules which are normally not ionizable using conventional mass spectrometric techniques. Ambient ions can also be directed to different substrates to make new materials. A recent study showed that metal nanoparticles can be synthesized by electrolytic spray deposition of coinage metals.

The main objective of the present work is to understand ambient ions and their behavior at different substrates and interfaces. The work focuses on the effects of substrates on the morphology of the materials made by ambient ion deposition. A slight change in the deposition substrate introduced one-dimensionality to the synthesized material. The present work also deals with how these advanced materials can be used for diverse applications like collecting contaminants of air and water, capturing atmospheric water, etc.

Introduction of a liquid interface as a deposition substrate had a drastic change on the fate of the materials. The current study shows that a free-standing metal nanoparticle-nanosheet (NPNS) could be made under ambient conditions at the air-liquid interface. These sheets can be used as highly active catalysts due to their enhanced active surface area. When these metal ions were subjected to deposition on a liquid suspension of 2D sheets, like reduced graphene oxide (RGO), they neutralized and coalesced to form solid metal sheets at room temperature. Hence, the formation of metals directly from its salts was possible under atmospheric conditions. Now, if the substrate reacts with incoming ions, it may lead to interesting materials. This was shown in the following part, where chemical drilling of MoS2 nanosheets was demonstrated using ambient silver ions.

The work shows how advanced nanomaterials can be used to simplify or enhance mass spectrometry. Platinum nanoparticle nanotubes (NP-NT) were shown to be a catalytic substrate for vapor phase explosive detection. The high catalytic activity of NP-NTs was attributed to the roughness of the nanotubes decorated by nanoparticles. They were also insoluble in most of the solvents; hence act as a stable substrate for many cycles of catalysis. Such modified substrates can also be used for different chemical reactions. For example, graphene oxide coated paper was used as a reactive substrate for oxidation of alcohols to acids. In these experiments, a paper substrate was modified by coating these materials on it and then paper spray ionization (PSI) mass spectrometry experiments were performed. PSI being a fast process, detection of short-lived intermediates was also possible.